1. Field of the Invention
The present invention relates to an apparatus and a method for detecting an intersymbol interference for use in a record reproduction apparatus.
2. Description of the Prior Art
It has been recently important to control a recording medium as magnetic recording has recently shown much progress and a writable optical disk has been realized for practical use, which has a high recording density. The higher recording density makes a recording margin narrow, and accordingly it is important to control a recording reproduction system.
In an optical recording, a light spot which has a power distribution expressed nearly by a Gaussian distribution is used for recording. A spot mark is recorded which extends at the bottom, and tends to vary easily in size with a variation in recording power. In addition, the optical recording widely uses a thermal recording medium and, therefore the recorded mark can be easily changed in shape by heat conduction. Therefore, the recording condition changes to reduce the signal amplitude, increasing the intersymbol interference. Therefore, it is also necessary to inspect the most suitable recording power for an optical recording medium. In order to know the most suitable condition, it is necessary to measure the degree of the intersymbol interference for evaluating the characteristics of the recorded medium.
Generally the characteristics of the recording reproduction system are evaluated by noise characteristics and frequency characteristics. These characteristics have been evaluated with a measurement in the frequency domain using a spectrum analyzer. For example, as an evaluation-.method, it is possible to reproduce a signal at the highest frequency and measure its C/N ratio (carrier to noise ratio).
However, the method mentioned above needs an inspection in the frequency domain with the spectrum analyzer and makes an automation measurement difficult. There is still a problem that the measurement at the frequency domain does not directly guarantees the characteristics in a time domain at which a signal is practically treated. For the purpose of knowing a practical margin with various variation factors, jitter in the time domain has been measured. For example, the measurement of jitter is disclosed in U.S. Pat. No. 3,648,688 which does not disclose a signal pattern for measuring an intersymbol interference but rather discloses a calculation of the standard deviation only. Such a measurement of total jitter is sufficiently helpful for evaluating whether or not the practical characteristics are suitable. However, according to the measurement of total jitter, it is difficult to recognize each jitter due to the variation of each of the various variation factors.